Recalibrating motor control apparatus



Aug. 29, 1950 c. A. HARTUNG RECALIBRATING mowon com'RoL APPARATUS FiledJan. '10. 194'? 3 Sheets-Sheet 2 7 a 9/ 8 -10 7 6 p77 H439 t 3 2 )3 8 4.3 H 75 3 W 8 2 7 FIG. 3

INVENTOR. A. HARTUNG 4- was 3 39 3e FIG. 5

A 20 NQN-GB 22A -1 ATTORNEY Aug. 29, 1950 c. A. HARTUNG RECALIBRATINGMOTOR CONTROL APPARATUS S Sheets-Sheet 3 Filed Jan. 10, 1947 INVENHR.CHARLES A.HARTUNG ATTORNEY Pnened'Au 29, 1950 RECALIBRATING MOTORCONTROL APPARATUS CharlesA. Hartung, Ridley Park, Pa., assignor, bymesne assignments, to Minneapolis-Honeywell Regulator Company,Minneapolis, Minn., a corporation of Delaware Application January 10,1947, Serial No. 721,242

Claims.

The present invention relates to measuring apparatus adapted to measureminute electrical currents or potentials, and, specifically, tomeasuring apparatus of the balanceable potentiometric, conversion type.More specifically, the invention relates to improved means formaintaining such potentiometric measuring apparatus continuouslystandardized.

A general object of the present invention is to provide improvedmeasuring apparatus of the balanceable potentiometric, conversion type.A more specific object of the present invention is to provide improvedmeans which are especially well suited for the production of a constantdirect potential for energizing the potentiometric measuring circuit ofsuch measuring apparatus. A still more specific object of the inventionis to provide means including a source of standard voltage for use inconnection with a potentiometric measuring circuit to supply to thelatter energizing voltage which is maintained at a constant value forextended periods of time, without the use of manual or automaticperiodic standardizing means as heretofore employed, and withoutsubjecting the source of standard voltage employed as a voltagereference to any objectionable current drain.

A further specific object of the invention is to provide constantvoltage energizing or continuous standardizing means for use withpotentiometric measuring apparatus which means comprises one or more ofthe main components of the measuring apparatus. Thus one or more of thecomponents of the measuring apparatus is utilized continuously to efiectboth measuring and standardizing operations. It is a still furtherspecific object of the present invention to provide, in connection withcontinuous automatic standardizing means for potentiometric apparatus,means utilizing a vibrating reed converter energized with alternatingcurrent for converting a unidirectional current into an alternatingcurrent having a frequency which is twice that of the energizingalternating current.

It has been recognized by those concerned with the measurement of minuteelectrical potentials by the potentiometer method, especially inconnection with the use of automatic or self-balancing potentiometers,that the voltage employed to energize the potentiometric circuit must bemaintained at a constant value, if the potentiometer is to be maintainedin calibration so that consistently accurate results can be obtained insuccessive measurements. It has also been found that the terminalvoltage of the dry cells customarily employed to energize self-balancingpotentiometric circuits decreases over the operative life of the cell tosuch an extent that it is not possible to so employ such cells inapparatus which is used to make measurements with a high degree ofaccuracy over extended periods of time without providing means forcompensating for this inherent instability of terminal voltage. Toaccomplish the maintenance of a constant potentiometric circuitenergizing voltage, various schemes have been used heretofore, the mostwidely used one being that wherein there is employed a standard cell andassociated manual or automatic periodic standardizing means. Suchstandardizing apparatus operates periodically, either under manual orautomatic control, effectively to compare the potentiometric energizingvoltage with the voltage of the standard cell and to adjust, ifnecessary, the former voltage with reference to the latter so that theenergizing voltage is maintained at a constant value.

The use of intermittent or periodic standardizing means has severalserious disadvantages. First of all, such automaticstandardizing mecha-.nism is necessarily complicated, while manual standardizing, though lesscomplicated, requires the attention of an operator. Secondly, with anyform of periodic standardizing, there will be periods between successivestandardizing operations during which the potentiometric energizingvoltage may change a sumcient amount to cause erroneous measurements tobe obtained in cases where high measuringaccuracy is extremelyimportant.

The present invention provides a form of standardizing which isparticularly well adapted for use with self-balancing potentiometricsystems and which provides continuous automatic standardizing, assuringa constant supply of energizing voltage to the potentiometric circuit atall times, and hence assuring highly accurate results in measurementsmade over extended periods of time.

In the operation of the present invention, the energizing voltagesupplied to the potentiometric circuit is continuously compared with thevoltage of a standard cell, and a variable resistor conthe measuring andstandardizing portions of a conversion type, self-balancingpotentiometric measuring system, and is operative to modifysimultaneously and continuously the signals in these two portions of thesystem. In another form of the illustrated embodiment of the invention,a single electro-mechanical, vibrating reed converter is utilized tomodify the measuring and standardizing signals simultaneously andcontinuously and to produce in a single channel electronic amplifier,which is common to both the measuring and standardizing portions of thesystem, corresponding alternating current signals, one of which has afrequency which is twice that of the other. One of these signals isutilized to produce continuous balance of the measuring system, and theother is utilized to maintain constant the potentiometric circuitenergizing voltage.

The various features of novelty which characterize this invention arepointed out with particularity in the claims annexed to and forming apart of this speciflcaton For a better understanding of the invention,however, its advantages and specific objects obtained with its use,reference should be had to the accompanying drawings and descriptivematter in which are illustrated and described preferred embodiments ofthe invention.

Of the drawings:

Fig. 1 is a circuit diagram illustrating a preferred embodiment of thepresent invention in connection with self-balancing potentiometricmeasuring apparatus of a well known type;

Figs. 2 and 3 are circuit diagrams illustrating two diiferentmodifications of the system of Fig. 1;

Fig. 4 is a circuit diagram illustrating another modification of thesystem of Fig. 1 in which is employed a standardizing control systemdiflerent from that of Fig. 1; and

Fig. 5 is a circuit diagram illustrating a modification of the system ofFig. 4.

There is illustrated in Fig. 1 the circuit diagram of a well known formof self-balancing potentiometric measuring apparatus of the typedisclosed and claimed in the copending U. S. Patent application ofWalter P. Wills, Serial No. 421,173, filed December 1, 1941, whichissued as Patent No. 2,423,540 on July 8, 1947. The system of Fig. 1comprises a potentiometric measuring circuit generally designated at I,a vibrating reed converter 2, an input transformer 3, an electronicvoltage amplifier 4, a power amplifier and motor drive circuit 5, and atwo phase reversible induction motor generally designated at 6. Theseunits operate together to effect the measurement of minuteunidirectional potentials in a manner described in detail in said Willspatent.

In Fig. 1, the potentiometric system is shown by way of illustration asbeing of the recording type connected to indicate and record theinstantaneous values of the temperature of a thermocouple 1 and of afurnace 8 in which the thermocouple 1 is located. To this end, thepotentiometric circuit i includes a slide-wire resistance 9 having asliding contact In which is mounted on a carrage H. The carriage II iscarried on, and moved laterally by, a threaded drive shaft I! which isconnected by a suitable mechanical linkage l3 to the rotor ll of themotor 6. The measuring system operates in a manner well known to thoseskilled in the art to cause the sliding contact In to be moved along theslidewire resistance 9 by operation of the motor 6 so that the contactID is positioned according to the instantaneous temperatures of thefurnace I. The carriage II also carries a marking element such as a penl5 which cooperates with a record sheet such as the chart ii to producethereon a continuous record of the various instantaneous furnacetemperatures over a period of time. The chart is is moved as a functionof time at a constant speed in a direction perpendicular to thedirection of travel of the pen I5 by suitable chart driving means suchas a synchronous motor l1.

In addition to the slide-wire resistance 9, the circuit 1 comprisesthree parallel-connected branches. The first of these isa measuringbranch, including three resistors i8, i9 and 20, connected in series.The slide-wire resistance 9 is connected in parallel with the resistorI9, the latter being located between the resistors II and 20. The secondparallel branch is an energizing branch including a battery 2i and avariable resistor 22, having a sliding contact 22A, connected in series.The third branch is a compensating branch, including a thermocouple coldjunction compensating resistor 23 and a standardizing resistor 24connected in series.

The vibrating reed converter 2 is of the type disclosed in said Willspatent and in U. S. Patent 2,398,341 granted to Walter P. Wills on April9, 1946, and disclosed and claimed in the copending application ofFrederick W. Side, Serial No.

421,176, filed December 1, 1941, which issued as Patent No. 2,423,524 onJuly 8, 1947.

The converter 2 comprises a vibrating reed 25 which carries a contact 28and which is maintained in a vibrating condition by the conjoint actionof an alternating current energized operating coil 27 and a permanentmagnet 28. Two stationary contacts 29 and 30 are so arranged relative tothe reed 25 and the contact 26 that the latter alternately engages thecontacts 29 and 30 as the reed is caused to vibrate by the coil 27 andthe magnet 28.

The transformer 3 is of the voltage step-up type, comprising a lowimpedance primary winding 3| and a high impedance secondary winding 32wound in the conventional manner upon a suitable core 33. The electronicvoltage amplifier 4 may be of any suitable type, such as the typedisclosed in said Wills patents. The amplifier l includes inputterminals 34 and 35, output terminals 36 and 31, and energizingterminals 38 and 39.

The power amplifier and motor drive circuit 5 may well be of the typedisclosed in said Wills patents, including input terminals l0 and tioutput terminals 42 and 43, and energizing terminals 44 and 45. Themotor 6 may also be of the type shown in said Wills patents, comprisingin addition to the rotor I a power winding l6 and a control winding 41.

In the system of Fig. 1, one terminal of the thermo-couple l isconnected by a conductor 48 to the sliding contact it of the slide-wireresistance 9. Connection to the contact I! is made through a collectorbar 49 with which the contact I0 is in continuous engagement. Theremaining thermocouple terminal is connected by means of a conductor 50to one end terminal of the transformer. primary winding 3! and to thestationary converter contact 30. The remaining end terminal of thewinding 3i is connected to the converter contact 26 through the reed 25,and is also connected to a point 5| which is the I corresponding to atemperature increase.

junction between the resistors 23 and 24 in the circuit i.

35 of the amplifier 4. The output terminals 36 and 31 of the latter arerespectively connected to the input terminals 40 and M of the circuit 5.The motor control winding 41 is connected between the output terminals42 and 43 of the circuit 5.

A voltage step-down transformer 52 is employed to supply alternatingenergizing current to the converter coil 21. The transformer 52comprises a low voltage secondary winding 53 and a line Voltage primarywinding 54. The coil 21 is connected across the winding 53, and thewinding 54 is connected between supply conductors 55 and 56 which are inturn connected to a suitable source of alternating current, not shown,The energizing voltage supplied by the conductors 55 and 56 is hereinassumed to be 115 volts A. (3., having a frequency of 60 cycles persecond.

The amplifier 4 receives energizing current from the conductors 55 and56, the energizing terminal 58 being connected to the conductor 55 by abranch conductor 51, and the terminal 39 being connected to theconductor 55 by a branch conductor 58. Likewise, the circuit 5 isenergized from the conductors 55 and 56, the energizing terminals 44 and45 being respectively connected by branch conductors 59 and G9 to thesupply conductors 56 and 55, respectively. The motor power winding 46 isconnected between the conductors 55 and 55 in series with a condenser6!. A condenser 62 is connected in parallel with the motor controlwinding 41.

When the slide-wire contact i is in the position along the slide-wireresistance 9 which corresponds to the then existing temperature of thethermocouple and furnace 8, the-potentiometric system is said to bebalanced, and no voltage appears between the potentiometric outputterminal and the output conductor 50. Consequently, no input voltage isapplied to the input transformer 3, and no signal is applied between theamplifier input terminals 35 and 35 or between the input terminals 40and 4| of the circuit 5. Under this condition, the circuit 5 producesbetween the output terminals 52 and 53 and across the motor controlwinding 47 a signal which acts on the rotor id to prevent rotation ofthe latter. Consequently. the contact i0 is prevented from movingrelative to the slide-wire resistance 9 as long as the system remainsbalanced.

Upon a subsequent increase in the temperature of the furnace 8 above thetemperature value at which the system was balanced as just described,the potentiometric circuit becomes unbalanced, and a unidirectionalvoltage appears in the output of the circuit i. between the point 5| andthe conductor iii], having a magnitude proportional to the magnitude ofthe temperature increase and hence to the extent of the potentiometriccircuit unbalance, and having a given polarity This voltage is appliedacross the input transformer primary winding 3i, but is periodicallyreduced to zero by the short-circuiting action of the converter contactsand which are respectively connected to the ends of the winding 3|.Since the converter coil 21 is energized with 60 cycle voltage, thevoltage appl ed across the primary winding 3| will pulse at the rate of60 times per second, with the result that an alternating current signalwill be developed across the secondary winding 32 having a magnitudeproportional to the magnitude of the temperature increase and to theextent of the potentiometric unbalance,

having a frequency of 60 cycles per second, and

having a given phase corresponding to a temperature increase.

The signal just described is applied to the input of the amplifier 4,wherein it is amplified, and the resulting signal is fed into the inputof the circuit 5. The latter then delivers to the motor control winding41 a signal of such phase and magnitude that the rotor i4 is caused torotate in such a manner as to drive the contact In along the slide-wireresistance Sup-scale or to the right in Fig. 1 to a new balance positioncorresponding to the new, increased temperature. When the contact 10 hasbeen moved into this position, the system is once morebalanced, and therotor l5 and contact I!) are prevented from further movement until asubsequent temperature change in the furnace 8 takes place.

Upon a subsequent decrease in the furnace temperature, the converse ofwhat has just been described takes place. Specifically, a unidirectionalvoltage appears between the point 5| and the conductor 50 having amagnitude proportional to the magnitude of the temperature decrease andhaving a polarity opposite to that corresponding to a temperatureincrease. By the conjoint action of the converter 2 and transformer 3,this voltage is converted into a 60 cycle alternating current signalwhich appears between the amplifier input terminals 35 and 35 having amagnitude proportional to the magnitude of the temperature decrease, andbeing of opposite phase with respect to the corresponding signalproduced by a temperature increase. The signal is amplifled by theamplifier 4 and is fed to the circuit 5, which delivers to the motorcontrol winding 51 a signal of such phase and magnitude that the rotori4 is caused to drive the contact i0 down-scale or to the left in Fig. 1to a new balance position corresponding to the new, decreasedtemperature. When the contact in has moved to this position, the systemis once more balanced,

and the rotor M and contact I 0 are prevented from further movementuntil a subsequent temperature change takes place.

The manner in which the apparatus of Fig. 1 herein described functionsto perform the operations outlined above is described in detail in theaforementioned Wills Patent No. 2,423,540, and hence no furtherdescription will be made herein. Moreover, the portion of the apparatusof Fig. 1 already described is practically identical to that disclosedand claimed in the aforementioned Wills application, except withreference to the transformer 3, which is slightly different from thatdisclosed in said Wills application, and with reference to the meansemployed to efiect standardization. The standardizing means shown inFig. 1 and about to be described forms the basis of the presentinvention and is that which is claimed herein.

The continuous automatic standardizing apparatus of Fig. 1 comprises astandard cell 53, an input transformer 54, an electronic voltageamplifier 65. a power amplifier and motor drive circuit 66, a two phasereversible induction motor 61,.and a mechanical linkage 68. Thetransformer 64 may be identical to the transformer 3, having a primarywinding 69 and a secondary winding 10 wound on a core H. The amplifier65 may be identical to the amplifier 4, having input terminals 12 and13, energizing terminals 14 and l5, and output terminals 18 and I1, andthe circuit 88 may be identical to the circuit 5, having input terminals18 and I9, energizing terminals 88 and 8|, and output terminals 82 and83. The motor 81 may be identical to the motor 8,- comprising a powerwinding 84, a control winding 85, and a rotor 86.

The amplifier 65, circuit 88, and motor power winding 84 are energizedfrom the conductors 55 and 58 through the respective branch supplyconductors 81, 88, 89, 98. 9|, and 82. A condenser 93 is connected inseries with the winding 84, and a condenser 94 is connected in parallelwith the motor control winding 85. The motor rotor 86 is mechanicallycoupled by means of the linkage 88 to the sliding contact 22A of thevariable resistor 22, which is connected in the potentiometric circuitenergizing branch. This coupling is such that rotation of the rotor 88in one direction moves the contact 22A along the resistor 22 to increasethe efi'ective resistance of the latter and hence decrease theenergizing current flowing in the potentiometric circuit l. Rotation ofthe rotor 86 in the opposite direction moves the contact 22A to decreasethe resistance of the resistor 22 and hence to increase thepotentiometric circuit energizing current.

' One terminal of the standard cell 68 is connected to one end of theresistor 24, this end being the one opposite that connected to the Theremaining standard cell terminal point is connected to the convertercontact 28 and to one end terminal of the primary winding 89 of thetransformer 64. The remaining end of this winding is connected to thepoint 5| of the circuit i.

The secondary winding 18 is connected across the input terminals 12 and13 of the amplifier 85, and the output terminals 16 and 11 of the latterare respectively connected to the input terminals 18 and 19 of thecircuit 86. The motor control winding 85 is connected across the outputterminals 82 and 83 of the circuit 88.

The resistance value of the resistor 24 is so chosen that when theenergizing current produced by the battery 2| and flowing in the circuitis of such magnitude that the voltage drop across the slide-wireresistance 8 has a predetermined, normal value, the voltage drop acrossthe resistor 24 is just equal to the E. M. F. of the standard cell.

As is evident from the description of the apparatus previously given,the resistor 24 and the standard cell 63 are connected in series withthe primary winding 69 of the transformer 84. This connection is made insuch a manner that the voltage drop across the resistor 24 opposes theE. M. F. of the standard cell 63, so that when this voltage drop is justequal in magnitude to the standard cell E. M. F., no current flows inthe primary windling 89. Therefore, when the energizing current flowingin the circuit and produced by the battery 2| is of the correct value toproduce the normal voltage drop across the slide-wire resistance 9, nocurrent flows through the winding 68, and no signal is applied to eitherthe amplifier 85 or the circuit 66. Under this condition thestandardizing circuit is balanced and the circuit 88 delivers to themotor control winding 85 a signal which acts to prevent rotation of therotor 86 and to prevent movement of the sliding contact 22A on theresistor 22.

If the terminal voltage of the battery 2| decreases below the valueresponsible for the balanced condition of the standardizing circuit asJust described, the energizing current flowing in the circuit I willdecrease in magnitude and consequently the voltage drop across theresistor 24 will decrease. This voltage drop will now not be equal andopposite to the standard cell E. M. F.. and hence a current will flow inthe transformer primary winding 69. This current will be a, pulsatingone however, due to the periodic short-circuiting action of theconverter contacts 28 and 28, which contacts are seen to beconnectedacross the winding 89.

.As a result of this pulsating current flowing through the winding 69,an alternating current signal will appear across the secondary winding18 and between the amplifier input terminals 12 and 13 having afrequency of 60 cycles per second, having amagnitude proportional to theextent of the energizing current decrease, and being of a given phasecorresponding to a decrease in potentiometric energizing current andbattery voltage.

The signal applied to the input of the amplifier is amplified therein inthe conventional manner and is applied between the input terminals 18and I8 of the power amplifier and motor drive circuit 86. The latterfunctions to produce in response to this signal a motor drive signalwhich is applied to the motor control winding 85. This drive signal isof such phase and magnitude as to cause the rotor 86 to rotate and tomove the sliding contact 22A along the resistor 22 in a direction todecrease the effective resistance of the latter and hence to increasethe potentiometer energizing current. The motor 6'! will continue tothus drive the contact 22A to increase the energizing current until thelatter has once more reached its normal value. When this occurs, thevoltage drop across the resistor 24 will once more be equal and oppositeto the standard cell E. M. F., no signal will be applied to theamplifier 65, the standardizing circuit will again be balanced, and thecontact 22A and rotor 88 will be prevented from having furthermotioniuntil a subsequent change takes place in the voltage of thebattery 2|.

If the terminal voltage of the battery 2| should increase, thestandardizing system will function in such a manner that the motor 61will drive the contact 22A to increase the effective resistance of theresistor 22 and hence decrease the potentiometric energizing current.This will continue until the energizing current is returned to itsnormal value and the standardizing circuit is once more in balance.

From the description Just given, it can be seen that the response of thestandardizing system to an unbalance of this system, due to a change inthe terminal voltage of the battery 2|, is analogous to the response ofthe potentiometric measuring system to an unbalance due to a change inthe temperature being measured by the thermocouple 1. Similarly, thmanner in which the standardizing system functions to restore theenergizing current of the potentiometric system to its normal value, andhence to rebalance the standardizing system, is analogous to the mannerin which the potentiometric measuring system functions to restore thecondition of zero potentiometric circuit output voltage, and hence torebalance the measuring system. It is to be noted. however, thatunbalance and rebalancing of the measuring system in no way affects thestandardizing system, and that rebalancing of thelatter in no wayaffects the measurements made by or the operation of the measuringsystem. This lat ter statement is true since the standardizing system isin continuous operation, and, therefore,

any minute change in the terminal voltage of the battery 2| iscompensated for by an adjustment of the resistor 22 before such a changecan affect the accuracy of the measurements made by the potentiometricmeasuring system.

In Fig. 2 there is shown a modification of the system of Fig. 1 whereinthere is employed a different form of measuring system input transformerand a different converter, for the purpose of providing a more desirablesignal in the measuring system. All apparatus and connections not shownin Fig. 2 are identical to the corresponding apparatus and connectionsof Fig. 1, and apparatus shown in Fig. 2 bearing reference charactersshown in Fig. 1 is identical to the corresponding apparatus of Fig. 1.

In Fig. 2, the transformer 3 of Fig. 1 is replaced by a transformer 95,having a split primary winding comprising sections 96 and 9?, and havinga secondary winding 98 and a core 99. The converter 2 of Fig. 1 isreplaced in Fig. 2 by a converter Hi comprising a vibrating reed IIwhich carries contacts I02 and I03, relatively stationary contacts I02,I05 and I06, a permanent magnet I01, and an operating coil I08. Theconverter I82 is identical to the converter 2 except for the inclusionof the moving contact I03 and the relatively stationary contact I 06 inthe converter 6W. The contacts are so arranged in the converter 5 00that the contacts I03 and it are in engagement whenever the contacts Hi2and Iiit are engaged, and the contacts I03 and MB are out of engagementwhenever the contacts I02 and I05 are engaged.

The point 5| of the potentiometric circuit I is connected to theconverter reed WI and through the latter to the converter contacts I02and I03. The point Si is also connected to one end terminal of thestandardizing system input transformer primary winding 69 as before. Theother end terminal of this winding is connected as before to one of theterminals of the standard cell 63, and is also connected to theconverter contact I 06. Thus the converter contacts I03 and I06 areconnected across the winding 59 in the same manner as are the contacts26 and 29 in Fig. 1.

ployed a different form of standardizing system input transformer and adifferent converter, for

. tus and connections not shown in Fig. 3 are iden- The conductor fromthe thermocouple i1 is connected to the junction between the endterminals of the sections 96 and ill of the split primary winding of thetransformer 95. The remaining end terminal of the winding section 96 isconnected to the converter contact Hit, and the remaining end terminalof the winding section St" is connected to the converter contact I05.The

converter coil I08 is energized with alternating current as before. Itcan be readily seen that as the converter reed vibrates under theinfluence of the coil I08, the primary winding sections 9.6 and 9? arealternately connected between the conductor 50 and the point 5i acrossthe output of the potentiometric measuring circuit I. Consequently, theoutput of the circuit I is not periodically short-circuited by theconverter contacts as it is in the arrangement of Fig. 1. The resultingsignal produced in the secondary winding 98 will be of more suitablewave form and will have a greater effective value than will thecorresponding signal produced by the Fig. 1 arrangement. Hence, themeasurements made with the apparatus of Fig. 2 will be inherently moreaccurate than corresponding measurements made with the apparatus of Fig.1.

In Fig. 3 there is illustrated another modification of the system ofFig. 1 wherein there is em- Kill tical to the corresponding apparatusand connections of Fig; l, and apparatus shown in Fig. 3 bearingreference characters shown in Figs. 1 and 2 is identical to thecorresponding apparatus of Figs. 1 and 2.

The input transformer of Fig. 2 is included in the potentiometricmeasuring system of Fig. 3. However, in the latter figure, thestandardizing system input transformer 64 of Figs. 1 and 2 is replacedby a transformer Hi9 This transformer is identical to the transformer25, comprising a split primary winding having sections H0 and l I I, andincluding a secondary winding H2 and a core II 3. The converter 2 ofFig. 1 is replaced in Fig. 3 by a converter II which is identical to theconverter 2 except for the addition of a sec-- ond movable contact and asecond pair of relatively stationary contacts. Thus the converter lidcomprises a vibrating reed H5 carrying a contact lit and a secondcontact ill. Cooperating with the contact IIE are relatively stationarycontacts H8 and I59, and cooperating with the contact iii are relativelystationary contacts I20 and IN. The converter II s also includes apermanent magnet I22 and an alternating current energized operating coilI23.

In the system of Fig. 3, the point 5i in the circuit I is connected tothe converter reed I I5- and through the latter to the movable contactsIifi and i II. The thermocouple conductor 50 is connected as before tothe junction between the end terminals of the primary winding sections96 and er, and the remaining end terminals of these sections arerespectively connected to the converter contacts H8 and M9. Thus thetransformer 95 and the potentiometric circuit I are connected to theconverter lit in the same manner as they are connected to the converterI20 of Fig. 2.

One terminal of the standard cell 63 is connected to one end of theresistor 2% as before, and the remaining standard cell terminal isconnected to the junction between the end terminals of the primarywinding sections H0 and III of the transformer ms. The remaining endterminals of these winding sections are respectively connected to theconverter contacts H9 and IN. The secondary winding H2 is connectedbetween the amplifier input terminals 72 and F3.

The contacts of the converter He are so arranged that the contacts H8and HG are engaged at the same time that the contacts I20 and iii areengaged. Likewise, the contacts H9 and M6 are engaged at the same timethat the contacts I26 and iii are engaged. Therefore, the primarywinding sections III] and Iii are alternately connected between thepoint SI and the terminal of the standard cellfiii which is notdidirectly connected to the resistor 24. It is evident that in theapparatus of Fig. 3, the resistor 25 and the standard cell 63 are neverdirectly connected in voltage opposition as they are by theshort-circuiting action of the converters 2 and Mil in Figs. 1 and 2,respectively. Consequently, the standard cell 63 is never subjected toan undesirable current drain.

The advantage of the arrangement of Fig. 3 over that of Fig. 2 is thatin the Fig. 3 apparatus a signal is produced in the secondary winding Il2 of the standardizing transformer I03 which has a better wave form anda greater eflective value than has the corresponding si nal which isproduced in the system of Figs. 1 and 2. This enables more perfectcontinuous standardizing to be accomplished than is obtained with thearrangements of Figs. 1 and 2.

In Fig. 4 there is illustrated another modification of the system ofFig. 1 in which is employed standardizing apparatus diflering from thatused in th Fig. 1 system. The potentiometric measuring circuit I,converter 2, thermocouple 1, voltage amplifier 4, power amplifier andmotor drive circuit 5, motor 5 and motor 51 of Fig. 1 are all includedand connected in the Fig. 4 arrangement as they are in that of Fig. 1.The system of Fig. 4 also includes the transformers 35 and I09 of Fig.3, a converter I24, an inductance I25, a resistor I26, and a poweramplifier and motor drive circuit I21, the latter replacing the voltageamplifier 55 and the circuit 55 of the arrangements of Figs. 1-3.

The converter I24 may be identical to the converter 2, comprising a reedI23 which carries a contact I29. an operating coil I30, a permanentmagnet I3I, and relatively stationary contacts I32 and I33. The circuit5 is shown as comprising an input transformer I34 having a primarywinding I35 and a secondary winding I35, two

triode electron tubes I31 and I33, each comprising a plate, a controlgrid, a cathode, and a cathode heater, and a power transformer I33having a primary winding I40, a cathode heater energizing winding HI,and a secondary winding I42.

In the circuit 5, the input terminals 40 and H are respectivelyconnected to the end terminals of the input transformer primary windingI35. One end terminal of the associated secondary winding I36 isconnected to the control grids of the triodes I31 and I33, and theremaining secondary end terminal is connected to the cathodes of thesetriodes and to the output terminal 43.

The remaining output terminal 42 is connected to a center-tap on thepower transformer secondary winding I42, and each of the end terminalsof the latter is respectively connected to one of the plates of thetriodes I31 and I38. The power transformer primary winding I40 isconnected between the energizing terminals 44 and 45, and the cathodeheater secondary winding MI is connected to the cathode heaters of thetriodes I31 and I38 by partially shown conductors X in such a manner asto supply the necessary energizingcurrents to these cathode heaters.

The form of the circuit 5 which is illustrated by way of example in Fig.4 is that disclosed in the aforementioned Wills patent. The circuit 5 ofFig. 4 is also disclosed in U. S. Patent 2,376,-

527 granted to Walter P. Wills on May 22, 1945, in connection withapparatus employing a circuit of the form of the circuit I21 of Fig. 4,about tobe described.

The power amplifier and motor drive circuit I21 is similar to thecircuit 5 except that the circuit I21 is responsive only to inputsignals having a frequency of 120 cycles per second to produce motordrive, whereas the circuit 5 is responsive only to input signals havinga frequency of 60 cycles per second to produce motor drive. The circuitI21 comprises an input transformer I43, having a primary winding I44 anda'secondary winding I45, triode electron tubes I43 and I41, each havinga plate, a control grid, a cathode, and a cathode heater, and a powertransformer I43 having a primary winding I43, a secondary windilrgI I50,and a cathode heater energizing winding Each of the end terminals of theinput transformer secondary winding I45 is respectively connected to oneof the control grids of the triodes I45 and I41. A center-tap on thewinding I45 is connected to the cathodes of these triodes and to one endterminal of the motor control winding 85. The remaining motor controlwinding terminal is connected to a center-tap on the power transformersecondary winding I50, and each of the end terminals of the latter isrespectively connected to one of the plates of the triodes I45 and I41.

The primary winding I43 of the power transformer I48 is connectedbetween the supply conductors 55 and 53 by means of branch conductorsI52 and I53, and the cathode heaters of the triodes I45 and I41 areconnected to the winding I5I and energized therefrom through thepartially shown conductors Y.

The potentiometric measuring portion of Fig. 4 is connected essentiallyas before, the point 5| of the circuit I being connected to theconverter contact 25, and the thermocouple conductor 50 being connectedto the junction of the end terminals of the primary winding sections 35and 91. The remaining end terminal of the winding 35 is connected to theconverter contact 30, and the remaining end terminal of the winding 31is connected to the converter contact 29.

The input portion of the stanardizing system is connected in a novelmanner which causes the signal developed inthe input transformersecondary winding II2 to have a frequency of cycles per second, which istwice the frequency of the voltage used to energize the converteroperatin coils 21 and I30. To this end, the converter contact I33 isconnected to one end terminal of the standardizing input transformerprimary winding III and to the point 5|. The converter contact I 32 isconnected to one end terminal of the winding I I0 and to one terminal ofthe standard cell 63. The remaining terminal oi the latter is connectedto one end of the resistor 24 as before, and the remaining end terminalsof the windings I I0 and III are connected together and to the convertercontact I29 only. The resistor I25 is connected between the convertercontacts I32 and I33 for improving the wave form of the output voltageof the converter I24.

As can be seen from Fig. 4, the primary winding sections IIII and III ofthe standardizing input transformer I09 are normally connected in serieswith the standard cell 53 and the standardizing resistor 24. Any currentproduced by a need for standardizing will therefore flow through thewindings H0 and III. However, as the converter contact I23 alternatelyengages the contacts I32 and I33, the windings H0 and III arealternately short-circuited, each winding being so short-circuited onceeach cycle of the converter energizing voltage. Since the convertercoils are energized with 60 cycle current, the short-circuitin of thetwo primary windings each cycle causes a 120 cycle signal to be producedin the secondary winding I I2 as a result of a need for standardizing.This signal correspondings to the 60 cycle signal produced in thewinding H2 in the apparatus of Fig. 3.

The converter coil I30 of the standardizing converter I24 is energizedin the same manner as are the operating coils of the other convertersdescribed herein, except for the fact that the respect to the supplyvoltage phase.

previously mentioned inductance I25 is connected in series with one ofthe conductors supplying the coil I30 with energizing current. Theeffect of this inductance is to cause the voltage supplied to the coilI30 to be shifted in phase with respect to the phase of the supplyvoltage for a purpose to be described hereinafter.

The secondary windings 98 and H2 of the respective transformers 95 andI09 are connected in series between the amplifier input terminals 34 and35. Therefore, when the measuring and standardizing circuits areunbalanced, a complex signal is applied between the input terminals 3 2and 35 consisting of a 60 cycle component from the transformer 95 andthe measuring circuit, representative of measuring circuit unbalance,and a 120 cycle component from the transformer I09 and the standardizingcircuit, representative of standardizin circuit unbalance. Due to theeffect of the reactor I25 in the coil energizing circuit of thestandardizing converter I2 2, the 120 cycle standardizing signalcomponent will be shifted in phase through 45 of the 60 cycle measuringsignal component for a reason to be described hereinafter.

The input terminal 8 of the power amplifier 1 and motor drive circuit isconnected as before to the amplifier output terminal 36. The primarywinding I l I of the transformer I43 of the standardizing poweramplifier and motor drive circuit I2? is connected between the amplifieroutput terminal 3? and the input terminal ii of the circuit 5. Thus theprimary windings I35 and I MI are connected in series between theamplifier output terminals 36 and 3?.

When either the 60 cycle signal or the 120 cycle signal or both areapplied to the input of the amplifier t, the amplified resultant of theinput signal will appear across both of the primary windings I35 and Iit and the secondary wind ings I36 and M5 in the usual manner. Asdescribed in detail in the aforementioned Wills Fatent No. 2,423,540 andin the Wills Patent 2,376,527, and mentioned hereinbefore, the circult 5is operative to produce a signal to cause operation of the motor 6 onlyin response to a 60 cycle input signal. Consequently, only a 6d cyclesignal across the winding I36 will produce motor drive in the motor a,the 120 cycle signal, if present, having no effect on the operation ofthe motor 6. Therefore, the circuit 5 and motor 5 respond to measuringcircuit unbalance to effect rebalancing of the measuring circuit in thesame manner as previously described.

As hereinbefore mentioned, the circuit I27. is operative to produce asignal to cause operation of the motor IiI only in response to a 120cycle input signal which is shifted in phase 45 with.

Consequently, only such a 120 cycle signal across the winding I 35 willproduce motor drive in the motor GI, the 60 cycle signal, if present,having no effect on the operation of the motor 67. Therefore, thecircuit I27 and motor B'I respond to standardizing circuit unbalance toeffect rebalancing of the standardizing circuit, and hence standardizingof the potentiometric system, in the same manner as previouslydescribed.

The operation of the circuit I2I whereby the latter produces motor drivesignals only in response to 120 cycle input signals is explained indetail in the aforementioned Wills Patent 2,376,527, and such operationwill therefore not be elaborated on herein. Suffice it to say that thecircuit I'2'I produces motor drive signals in response to 120 cycleinput signals of the correct phase, which motor drive signals areidentical to motor drive signals produced by the circuit 5 in responseto equivalent cycle input signals. Such operation will be apparent tothose skilled in the art when considered in connection with thedescriptions given herein.

An important advantage of the system of Fig. 4 over the systemspreviously disclosed herein is that in the Fig. 4 arrangement only onevoltage amplifier is employed, the amplifier being eliminated from thisapparatus. In Fig. 4, the amplifier 4 serves the dual purpose ofamplifying both the measuring circuit and the standardizing circuitunbalance signals.

There is illustrated in Fig. 5 another modification of the apparatus ofFig. 1 wherein a single converter of the type employed in the Fig. 2 ar=rangement replaces the two converters 2 and IM of Fig. 4. To this end,the system of Fig. 5 includes the measuring circuit I and the inputtransformer 3 of Fig. l, the converter IflIi of Fig. 2, and thestandardizing input transformer Hit of Figs. 3 and 4. The Fig. 5arrangement also includes the thermocouple I, the standard cell t3 andthe amplifier Ll. All f the components and connections in the circuit ofFig. 5 past the output of the amplifier s and not shown in Fig. 5 arethe same as the corresponding components and connections as illustratedin Fig. 4.

' In the arrangement of Fig. 5, the point SI in the circuit I isconnected to one end terminal of the input transformer primary windingM. This point is also connected to the converter contact Hit, and to oneend terminal of the standardizing input transformer primary wind ingsection lit. The remaining end terminal of the primary winding as isconnected to the converter contact its and to the thermocouple conductor5d. The remaining end terminal of the winding II) is connected to theadjacent terminal of the winding III and to the movable convertercontacts It? and I03. The remaining terminal of the winding III isconnected to the converter contact Hi5 and to one terminal of thestandard cell 63. The other terminal of the latter is connected to theresistor 2 as before.

The secondary winding 32 of the transformer 3 is connected between theamplifier input terminals 3d and 35. The secondary winding IE2 of thetransformer I09 is connected in series with a condenser its between theterminals 3t and 35. The value of this condenser is so chosen that thesignal from the winding I I 2 is caused to be displaced 45 in phase fromthe signal from the winding 32.

From the description just given it can be seen that the convertercontacts its and Hit are connected acros the primary winding 3i.Therefore, as the converter operates in the normal manner, the winding3i is short-circuited once every cycle of the supply voltage, ashereinbefore described in connection with the arrange-- ment of Fig. 1.Consequently, a 60 cycle signal representative of measuring circuitunbalance will appear across the secondary winding 32 and across theinput of the amplifier d as before. It can also be seen that theconverter contacts HM and I02, and I05 and I02 alternately shortcircuittheir respective primary winding sections H0 and III, each of the latterwinding sections being so short-circuited once each cycle of the supplyvoltage, as described in connection with the Fig. 4 arrangement.Consequently, a 126 cycle signal representative of standardizing circuit unbalance will appear across the secondary winding H2 as in theFig. 4 arrangement. Since this last mentioned signal passes through thecondenser I54, it is shifted in phase 45 with respect to the 60 cyclesignal and the supply voltage, as is necessary for the requiredoperation of the power amplifier and motor drive circuit I21.

Since in the system of Fig. 5 there are produced in the input of theamplifier 4 a 60 cycle signal representative of measuring circuitunbalance and a 120 cycle signal representative of standardizing circuitunbalance, the operation of this system is identical to that of the Fig.4 arrangement, previously described. The Fig. 5 arrangement does possessthe advantage over that of Fig. 4 of utilizing only one converter forboth the measuring and standardizing circuits. It may be noted that thearrangements disclosed herein for providing continuous automaticstandardizing may be effectively employed when the energizing battery 2|is replaced by a rectifier and a suitable source of alternating currentas potentiometric circuit energizing means.

Subject matter disclosed but not claimed herein is disclosed and claimedin my copending U. S. patent application, Serial No. 102,193, filed June30, 1949.

While, in accordance with the provisions of the statutes, I haveillustrated and described the best forms of embodiment of the inventionnow known to me, it will be apparent to those skilled in the art thatchanges may be made in the form of the apparatus disclosed withoutdeparting from the spirit of the invention as set forth in the appendedclaims, and that in some cases certain features of the invention maysometimes be'used to advantage without a corresponding use of otherfeatures.

Having now described my invention, what I claim as new and desire tosecure with Letters Patent is:

1. Measuring apparatus including a pair of terminals adapted to beconnected to a source of voltage to be measured, a balanceablepotentiometric measuring circuit including an adjustable resistor andadapted to produce a first output signal representative of the value ofthe voltage to be measured, a source of variable energizing voltage, asource of standard voltage, connections between said measuring circuit,said source of variable energizing voltage, and said source of standardvoltage whereby a voltage drop is produced across said resistor andwhereby said measuring circuit is operative to produce a second outputsignal representative of the value of the voltage drop across saidresistor, converting and amplifying means having an input circuitadapted to receive both of said output signals and having a singleelectromagnetic, vibrating reed converter adapted to modifysimultaneously and continuously both of said output signals, balancingmeans connected to said converting and amplifying means and responsiveto said first output signal to adjust said resistor continuously tomaintain said measuring circuit in continuous balance, and a reversibleelectric motor connected to said converting and amplifying means andresponsive to said second output signal continuously to maintainconstant the voltage drop across said resistor.

2. In measuring apparatus, the combination of a balanceabiepotentiometric measuring circuit including a fixed resisto and avariable resistor having a sliding contact which engages said variableresistor, a source of energizing voltage for said measuring circuit, anadjustable resistor connected in series between said circuit and saidsource or energizing voltage and adapted to control the magnitude of theenergizing voltage supplied to said circuit, whereby voltage drops areproduced across said variable resistor and said fixed resistor which aredependent in magnitude on the adjustment of said adjustable resistor, asource of standard voltage, a pair of terminals adapted to be connectedto a source of voltage to be measured, first control means operativecontinuously to position said sliding contact on said variable resistorin accordance with the magnitude of the voltage being measured tomaintain said measuring circuit continuously balanced and comprising atransformer having a primary winding connected in series with a portionof said measuring circuit between said terminals and having a secondarywinding, second control means operative continuously to adjust saidadjustable resistor to maintain constant the voltage drop across saidvariable resistor and comprising a second transformer having a primarywinding in series with which-are connected said source of standardvoltage and said fixed resistor and having a secondary winding, andconverting means common to both said first and second control means andcomprising an electro-mechanical, vibrating reed converter having amovable contact, two stationary contacts, and an operating coil adaptedto be energized with alternating current and operative to move saidmovable contact into and out of engagement with one of said stationarycontacts once during the first half of each cycle of the alternatingcurrent and to move said movable contact into and out of engagement withthe other of said stationary contacts once during the second half ofeach cycle of the alternating current, said movable contact beingelectrically connected to one end of each of said primary windings, saidone stationary contact being electrically connected to the other end ofone of said primary windings, and said other stationary contact beingelectrically connected to the other end of the other. of said primarywindings, whereby a first alternating current signal is produced acrossone of said secondary windings and a second alternating current signal,having a frequency the same as that of the first signal, is producedacross the other of said secondary windings.

3. In measuring apparatus, the combination of a balanceablepotentiometric measuring circuit including a fixed resistor and avariable resistor having a sliding contact which engages said variableresistor, a source of energizing voltage for said measuring circuit, anadjustable resistor connected in series between said circuit and saidsource of energizing voltage and adapted to control the magnitude of theenergizing voltage supplied to said circult,' whereb voltage drops areproduced across said variable resistor and said fixed resistor which aredependent in magnitude on the adjustment of said adjustable resistor, asource of standard voltage, a pair of terminals adapted to be connectedto a source of voltage to be measured, first control means operativecontinuously to position said sliding contact on said 5 variableresistor in accordance with the magnitude of the voltage being measuredto maintain said measuring circuit continuously balanced and comprisinga transformer having a center-tapped primary winding and a secondarywinding, second control means operative continuously to adjust saidadjustable resistor to maintain constant the voltage drop across saidvariable resistor and comprising a second transformer having acenter-tapped primary winding and a secondary winding, converting andamplifying means common to both said first and second control means andcomprising a single channel electronic voltage amplifier andfirst andsecond electro-mechanical, vibrating reed converters, each of saidconverters having a movable contact, two stationary contacts, and anoperating coil adapted to be enthe primary winding of said firsttransformer, an

electrical connection between the other end of the latter and the otherstationary contact of said first converter, a connection including saidterminals and a portion of said measuring circuit connected in seriesbetween the movable contact "of said first converter and the center-tapof the primary winding of said first transformer, an electricalconnection between one of the stationary contacts of said secondconverter and one end of the primary winding of said second transformer,an electrical connection between the other end of the latter and theother stationary contact of said second converter, said source ofstandard voltage and said fixed resistor being connected in series withthe primary winding of said second transformer independently of thecontacts of said second converter, and an electrical connection betweenthe center-tap of the primary winding of said second transformer and themovable contact of said second converter, whereby a first alternatingcurrent signal is produced across the secondary winding of said firsttransformer and a second alternating current signal, having a frequencywhich is twice that of the first signal, is produced across thesecondarywinding of said second transformer.

a. In measuring apparatus, the combination of a balanceablepotentiometrio measuring circuit including a fixed resistor and avariable resistor having a sliding contact which engages said vari: ableresistor, a source of energizing voltage for said measuring circuit, anadjustable resistor con-, nected in series between said circuit and saidsource of energizing voltage and adapted to con trol the magnitude ofthe energizing voltage sup= plied to said circuit, whereby voltage dropsare produced across said variableresistor and said fixed resistor whichare dependent in magnitude on the adjustment of said adjustableresistor, a source of standard voltage, a pair of terminals adapted tobe connected to a source of voltage to be measured, first control meansoperative continuously to position said sliding contact on said acrosssaid variable resistor and comprising a second transformer having acentertapped primar winding in series with which are connected saidsource of standard voltage and said fixed resistor and having asecondary winding, converting and amplifying means common to both saidfirst and second control means and comprising a single channelelectronic volta e amplifier and an electro-mechanical, vibrating reedconverter having a movable contact, three stationary contacts, and anoperating coil adapted to be energized with alternating current andoperative to move said movable contact into and out of simultaneousengagement with two of said stationary contacts once during the firsthalf of each cycle of the alternating current and to move said movablecontact into and out of engagement with the other of said stationarycontacts once during the second half of each cycle of the alternatingcurrent, an electrical connection between one of said two stationarcontacts and one end of the primary winding of said first transformer,an electrical connection between the other end of the latter and theother of said two stationary contacts, an electrical connection betweenthe last mentioned contact and one end of the primary winding of saidsecond transformer, an electrical connection between the other end ofthe latter and said other stationary contact, and an electricalconnection between the center-tap of the primary winding of said secondtransformer and said movable contact, whereby a first alternatingcurrent signal is produced across the secondary winding of said firsttransformer and a second alternating current signal, having a frequencywhich is twice that of the firstsignal, is produced across the secondarywinding of said second transformer.

5. In measuring apparatus, the combination of an adjustable measuringcircuit including a source of variable energizing voltage and adapted toproduce unidirectional measuring output signals which are representativeof the values of a quantity being measured and to produce unidirectionalstandardizing output signals which are representative of variations insaid energizing voltage, an amplifying and motor drive circuit having aninput circuit including said measuring circuit, having two outputcircuits, andhaving at least one portion adapted to modify con tinuouslyand simultaneously both of said output signals and including anelectro-mechanical, vibrating reed converter adapted to convert saidmeasuring output signals into pulsating signals and to convert saidstandardizing output signals into other pulsating signals, a firstreversible electric motor connected in one of said output circuits andadapted to adjust continuously said measuring circuit in response to themodified measuring output signals, and a second reversible electricmotor connected in the other of said output circuits and adapted to varysaid energizing voltage in response to the modified standardizing outputsignals to maintain the energizing voltage constant at a predeterminedvalue.

6. In measuring apparatus, the combination of an adjustable measuringcircuit including a source of variable energizing voltage and adapted toproduce unidirectional measuring output signals which are representativeof the values of a quantity ,being measured and to produceunidirectional standardizing output signals which are representative ofvariations in said energizing voltage, an amplifying and motor drivecircuit having an input circuit including said measuring circuit, havingtwo output circuits, and having at least one portion adapted to modifycontinuously and simultaneously both or said output signals andincluding an clcctro-mechanical, vibrating reed converter adapted toconvert said measuring output signals intopulsating signals and toconvert said standardizing output signals into other pulsating signalshaving a frequency of pulsation which is the same as that of the firstmentioned signals, a first reversible electric motor connected in one ofsaid output circuits and adapted to adjust continuously said measuringcircuit in response to the modified measuring output signals, and asecond reversible electric motor connected in the other of said outputcircuits and adapted to vary said energizing voltage in response to themodified standardizing output signals to maintain the energizing voltageconstant at a predetermined value.

7. In measuring apparatus, the combination of an adjustable measuringcircuit including a source of variable energizing voltage and adapted toproduce unidirectional measuring output signals which are representativeof the values of a quantity being measured and to produce unidirectionalstandardizing output signals which are representative of variations insaid energizing voltage, an amplifying and motor drive circuit having aninput circuit including said measuring circuit, having two outputcircuits, and having at least one portion adapted to modify continuouslyand simultaneously both of said output signals and including a singlechannel, electronic voltage amplifier and a single electro-mechanical,vibrating reed converter, said converter being adapted to convert saidmeasuring output signals into pulsating signals and to convert saidstandardizing output signals into other pulsating signals having afrequency of pulsation which is substantially dlilerent from that of thefirst mentioned pulsating signals, and said amplifier being arranged toamplify both of said pulsating signals, a first reversible electricmotor connected in one of said output circuits and adapted to adjustcontinuously said measuring circuit in response to the modifiedmeasuring output signals, and a second reversible electric motorconnected in the other of said output circuits and adapted to vary saidenergizing voltage in response to the modified standardizing outputsignals to maintain the energizing voltage constant at a predeterminedvalue.

8. Measuring apparatus of the type including a pair of terminals adaptedto be connected to a source of voltage to be measured, a balanceablepotentiometric measuring circuit connected to said terminals, a sourceof variable energizing voltage adapted to apply energizing voltage tosaid circuit, first electronic converting, amplifying, and control meansadapted to maintain said circuit continuously balanced, and secondelectronic converting, amplifying, and control means adapted to maintainconstant the energizing voltage applied to said circuit from said sourceof energizing voltage, said second electronic means including areversible electric motor adapted to vary the energizing voltage appliedto said circuit and including a single electro-mechanical, vibratingreed converter which is common to both said first and second electronicmeans and which is operative to produce alternating current signalswhich are utilized to maintain said circuit continuously balanced and tomaintain constant the energizing voltage applied to said circuit.

9. In measuring apparatus, the combination of including a fixed-resistorand a variabbrclhhl' having a sliding contact which engages saidvariable resistor, a source of energizing voltaufor said measuringcircuit, an adjustable resinconnected in series between said circuit andsaid source of energizing voltage and adapted to control the magnitudeoi the energizing voltage supplied to said circuit, whereby voltagedrops are produced across said variable resistor and said fixed resistorwhich are dependent in magnitude on the adjustment of said adjustableresistor, a first pair of terminals between which are connected a sourceof voltage to be measured and a portion of said measuring circuit, asource of standard voltage, a second pair of terminal between which areconnected said source of standard voltage and said fixed resistor, firstcontrol means operative continuously to position said sliding contact onsaid variable resistor in accordance with the magnitude of the voltagebeing measured to maintain said measuring circuit continuously balanced.said first control means having an input circuit which includes saidfirst pair of terminals and having an output connectiim which isoperative to position said sliding contact, and second control meansoperative continuous- 1y to adjust said adjustable resistor to maintainconstant the voltage drop acres said variable resistor, said secondcontrol means having an in? put circuit which includes said second pairof terminals, having a reversible electric motor connected to saidadjustable resistor and operative to adjust the latter, and including asingle electro-mechanical, vibrating reed converter which is common toboth said first and second control means and which is operative toproduce alternating current signals which are utilimd to maintain saidmeasuring circuit continuously balanced and to maintain constant thevoltage drop across said variable resistor.

10. In measuring apparatus, the combinatim of a balanceablepotentiometric measuring circuit including a fixed resistor and avariable re-' sistor having a sliding contact which enga e! saidvariable resistor, a source of energizing voltage for said measuringcircuit, an adjustable resistor connected in series between said circuitand said source of energizing voltage and adapted to control themagnitude of the energizing voltage supplied to said circuit, wherebyvoltage drop are produced across said variable resistor and said fixedresistor which are dependent in nitude on the adjustment of saidadjustable resistor, a first pair of terminals between which areconnected a source of voltage to be measured and a portion of saidmeasuring circuit, a source of standard voltage, a second pair ofterminals be-- tween which are connected said source of standard voltageand said fixed resistor, first control means operative continuously toposition said sliding contact on said variable. resistor in accordancewith the magnitude of the voltage bein measured to maintain saidmeasuring circuit continuously balanced, said first control means havingan input circuit which includes said first pair of terminals and havingan output connection which is operative to position said slidingcontact, and second control means operative continuously to adjust saidadjustable resistor to maintain constant the voltage drop across saidvariable resistor, said second control means having an input circuitwhich includes said second pair of terminals, having a reversibleelectric motor connected to said adjustable resistor and a balanceablepotentiometric measuring circuit operative to adjust the latter, andincluding a age drop across said variable resistor and which 10 has afrequency which is substantially diiferent from that oi said firstalternating current signal, and said amplifier being operative toamplify simultaneously and continuously both of said alternating currentsignals.

CHAR-LB A. HARTUNG.

22 nurnm-mcus crmn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Garstang July 6, 1937 GarstangAug. 11, 1942 Wills May 22, 1945 Wills Sept. 25, 1945 Schmitt Sept. 23,1947

